Biogenic magnetic nano hydroxyapatite: Sustainable adsorbent for the removal of perchlorate from water at near-neutral pH

The present work focuses on the utilization of biowaste material for a sustainable environment. In order to support the concept of 'value-added product from waste', Eggshell waste, which is a rich source of calcium is considered as a sustainable and renewable precursor for the synthesis of porous hydroxyapatite. This study introduces a novel, green and facile method for the synthesis of highly porous nano hydroxyapatite (nHA) and its magnetic composite aerogels (SPIONS@nHA) by freeze-drying technology. The synthesized materials have undergone through characterization. Perchlorate removal efficiency of the materials was investigated for the first time and the factors that influence the perchlorate adsorption capacity were explored and optimized. The magnetic composite of nHA showed an excellent separation in the presence of an external magnetic field from contaminated water after adsorption. XPS analysis and zeta potential measurements showed that the main driving force behind the adsorption of perchlorate is ion exchange and ion-pair formation/electrostatic interaction. Very fast removal kinetics was observed and the experimental maximum adsorption capacity for nHA and SPIONS@nHA were 148.4 and 305.8 mgg(-1) respectively. It is commendable that other commonly existing ions exhibited no remarkable effect on the adsorption performance, indicating SPIONS@nHA has an immense application potential. The adsorption process was found to follow by pseudo-second-order and intra-particle diffusion kinetic models. A novel method for the regeneration of perchlorate loaded adsorbent using phosphate buffer was also studied in this paper. The regeneration performance of spent magnetic adsorbent showed greater than 90% recovery on the adsorption capacity even after fifth cycle, revealing the stability, reusability and economic efficiency of the adsorbent. Thus, magnetic nanocomposite of the biogenic hydroxyapaptite can be exploited as a sustainable and efficacious material for the abolishment of perchlorate from aqueous media at near neutral pH.

Automated summary

The study focuses on utilizing eggshell waste to synthesize porous hydroxyapatite and magnetic composite aerogels through freeze-drying technology. The magnetic composite material shows high perchlorate removal efficiency, with ion exchange and ion-pair formation as the main driving force behind the adsorption process. The adsorption process follows pseudo-second-order kinetics, and the regeneration performance of the spent magnetic adsorbent demonstrates stability and high recovery rates after multiple cycles.